Xanthan gum is used widely in a number of industrial fields such as in oil-well drilling, in the ceramic industry, and in the paint industry. However, its performance characteristics can deteriorate even during storage at room temperature; such tendency becomes significant at higher temperatures and, in extreme cases, the use thereof for the intended purpose becomes impossible.
For example, in the case of petroleum recovery from an underground oil stratum by introducing under pressure an aqueous solution of xanthan gum, the oil stratum temperature generally reaches about 40.degree. to 100.degree. C. and the aqueous xanthan gum solution injected stays in the underground oil stratum from the injection well to the production well for a long period of time, for example several months to several scores of months. Therefore, guarantee of the quality of xanthan gum during such stay period is required. Xanthan gum is also used widely as a modifier for the mud-laden fluid for mud drilling in searching for petroleum. However, as a result of the increase in the depth of drilling in recent years, the stratum temperature reaches 90.degree. C. or higher, so that xanthan gum is decomposed and loses its function as a modifier for the mud-laden fluid, possibly leading to serious difficulties in drilling operations. For xanthan gum to fully achieve the intended purpose of its use, it is necessary to minimize the change in quality of xanthan gum in the above temperature range.